Barcode readers or scanners are found in many commercial environments such as, for example, point-of-sale stations in retail stores and supermarkets, inventory and document tracking, and diverse data control applications. To meet the growing demands, barcode symbol readers of various types have been developed for scanning and decoding barcode symbol patterns and producing symbol character data for use as input in automated data processing systems. Barcode scanners generally are available in hand-held, hands-free or in-counter formats.
One type of conventional barcode scanner is a laser scanner that generates a light beam which is scanned across a barcode. Light is reflected back to the scanner from the barcode. The reflected light is collected by a light-sensitive photodetector such as a photodiode which generates voltage signals corresponding to the varying intensity of the received light. The photodiode has associated circuitry that converts the analog light wave signals into a digitized signal representing the barcode. The digitized signal is then decoded by the circuitry and the barcode is interpreted or read.
Conventional laser barcode scanners include a laser source or generator such as a solid state visible laser diode (VLD) that generates a visible laser beam directed at the target barcode. The laser beam may be focused and collimated to produce a scanning beam for reading the target barcode. In some designs, the laser beam is projected onto and reflected from a mirrored device having a one-sided central spinning or rotating mirror that produces a raster or rasters comprised of multiple scanning lines each. These designs generally include a single laser beam which is projected onto one side of the spinning or rotating mirror (“spinner”), and then in turn onto the multiple stationary pattern mirrors as the laser beam is reflected from the spinner to produce a scanning pattern or raster field. The number of scanning beams or lines produced in the raster field and pattern affects the scanning efficiency, with generally the more lines and/or various high-density scanning patterns producing greater effectiveness in reading the target barcode when presented to the scanner in various orientations. Some examples of these central spinner type laser scanners are shown in U.S. Pat. Nos. 4,971,410; 5,196,696; and 5,221,832, which are incorporated herein by reference in their entireties.
Another type of laser scanner employs a rotating mirrored polygon having a plurality of mirrored facets disposed at various angles to each other. The laser is projected onto the rotating polygon and then in turn onto stationary pattern mirrors as the laser beam is reflected from the polygon to produce a scanning pattern or raster field. Some examples of the foregoing mirrored polygon designs are shown in U.S. Pat. Nos. 7,431,215 and 6,129,280, which are incorporated herein by reference in their entireties.
Some of the possible scanning patterns produced by the foregoing laser scanners are shown for example in U.S. Pat. No. 5,988,508, which is incorporated herein by reference in its entirety. The possible patterns produced include various raster patterns and high-density scanning patterns that may include rotating line, rosettes, and various Lissajous patterns. These various patterns are produced by varying the number, type, placement, and orientation of the mirrors.
The foregoing conventional rotating scanning polygons having multi-faceted pattern mirrors, however, have drawbacks. The mirrored polygons and their related mirrored facets are sometimes difficult to mold with precision and repeatability because of the upward and downward facing facets. Accordingly, an improved laser scanning system is desired.